Weed Science


PNW weed identification module

Listed below are profiles of many commonly found weeds in nurseries and field production sites throughout the Pacific Northwest, including Oregon, Washington, Idaho, and Northern California. Use this data base to assist with the identification of problem weeds you may encounter in your own fields, nursery or landscapes. More weeds profiles will be added as often as possible.Canada thistle flower

Each weed profile provides basic biological traits and cultural preferences for that weed, but for control and management options, we direct users to the Pacific Northwest Weed Management Handbook.

The easiest way to use this handbook is to look under the “Contents” tab on the drop-down menu across the top of the home page. Under this tab, the user can select from various crop type categories such as Christmas trees, Nursery, Greenhouse and Bulb crops, or Turfgrasses. Select the appropriate crop category, click and find valuable information for developing a working strategy for weed management.

Recommendations in this handbook are based on research results from the Agricultural Experiment Stations and Extension Services of Oregon, Idaho, and Washington. It is designed as a quick reference guide for weed control practices and herbicides used in various cropping systems and sites in our Pacific Northwest area.

The Pacific Northwest Weed Management Handbook is an invaluable resource, providing information and useful tools to assist growers and other industry professionals. Check out the tabs on Pesticide Safety, Tables and Calculations, as well as a Safety Checklist.

Weed ID

Annual bluegrass
Poa annua
In the Pacific Northwest, annual bluegrass usually germinates in late summer through spring when moisture is adequate.  Annual bluegrass generally forms small clumps of grass that can overcome a small nursery container if left untreated. Image by: James Altland, USDA-ARS
Annual Sowthistle
Sonchus oleraceae
Annual sowthistle is a very common weed in northwest field nurseries. Because it can germinate quite rapidly, it can quickly become problematic in agricultural areas.  Annual sowthistle flower heads occur in clusters called corymbs. Image by:James Altland, USDA-ARS
Cardamine oligosperma
Bittercress is most problematic in propagation and overwintering of crops. It is most prolific from late fall through early spring.  Bittercress can be problematic in container nursery settings. Image by: James Altland, USDA-ARS
Bittersweet Nightshade
Solanum dulcamara
Bittersweet nightshade is a perennial vine that easily forms into a rambling shrub if not controlled. It is a native of Europe and is also known as woody nightshade or simply bitter nightshade.  Bittersweet nightshade has large clusters of small, five petal flowers. Image by: James Altland, USDA-ARS
Bristly Hawksbeard
Crepis setosa
Bristly hawksbeard is common weed in landscapes, lawns and unmanaged areas. It is easily confused, particularly in the rosette stage, with other members of the Asteraceae family. The rosette and upright habit of bristly hawksbeard. Image by:James Altland, USDA-ARS
Broadleaf Dock
Rumex obtusifolius
Broadleaf dock, a perennial in the buckwheat family, has large, thick tap root. Broadleaf dock with flowering stalks. Image by: James Altland, USDA-ARS
Bull thistle
Cirsium vulgare
Bull thistle is one of the most common thistles the Northwest. In fact, the specific name vulgare means 'common'. Bull thistle flower heads are pink to purple, and approximately 1 inch tall and wide. Image by: James Altland, USDA-ARS
Canada thistle
Cirsium arvense
Canada thistle is extremely difficult to kill. A single plant can develop a lateral root system with a 20 foot spread in a single season. Thistle in field. James Altland, USDA-ARS
Common chickweed
Stellaria media
Common chickweed is primarily a winter annual broadleaf in the Pacific Northwest, but in some coastal areas, it can survive year-round. Prostrate habit of common chickweed. James Altland, USDA-ARS
Common groundsel
Senecio vulgaris
Although groundsel is a winter annual, it is very adaptable and often germinates and grows year round in Oregon's generally milder climate.  Common groundsels thick, fleshy green foliage is 2 to 4 inches in length, lacerate (irregularly lobed) and serrate. Image by: James Altland, USDA-ARS
Creeping woodsorrel
Oxalis corniculata
Creeping woodsorrel is one of the Oxalis species commonly found in Oregon nurseries and landscapes. Image by: James Altland, USDA-ARS
Curly Dock
Rumex crispus
Curly dock is a perennial weed with a large, deep taproot.It originated in Europe and is found throughout the United States. A mature Curly dock plant can have flowering stalks reaching up to 4 feet.
Taraxacum officinale
Dandelion is a hardy perennial which can be persistent in ornamental crops.  Flowers generally grow several inches above the foliage, however, in regularly mowed lawns, flowers will form on very short stal James Altland, USDA-ARS
Field bindweed
Convolvulus arvensis
Field bindweed is a deep-rooted perennial in the Morning-glory family.  Field bindweed is a vine with a spreading and climbing habit. It is one of the most difficult to control weeds in Oregon. James Altland, USDA-ARS
Field Horsetail
Equisetum arvense
Field horsetail is a perennial weed which is native to the Pacific Northwest. It is also one of the most difficult-to-control weeds in nursery crops.  When mature, plants can reach a height of 3 feet tall, but are usually much smaller. Image by:James Altland, USDA-ARS
Conyza canadensis
Horseweed is sometimes referred to as marestail. It is commonly a tall, erect summer annual weed.  Horseweed sometimes branches low near the soil, but rarely branches above. Image by: James Altland, USDA-ARS
Marchantia polymorpha
Liverworts are not vascular plants, but a more primitive life form similar to mosses. They do not have true leaves like most plants.  Liverwort thrive in moist container environments with top-dressed fertilizer. Image by: James Altland, USDA-ARS
Mouseear chickweed
Cerastium vulgatum
As the name suggest, mouseear chickweed leaves are oblong, fleshy with pointed tips and prominent hairs or fuzziness-resembling mouse ears.  Mouseear chickweed has a low growing, mounding habit. Leaves are fleshy and pubescent. James Altland, USDA-ARS
Northern willowherb
Epilobium ciliatum
Regionally, northern willowherb is known by several other common names, hairy willowherb, slender willowherb, or fringed willowherb.  Notice the distinctly sunken veins on the leaves and sometimes red coloration of the foliage. Image by: James Altland, USDA-ARS
Sagina procumbens
Pearlwort grows most aggressively in containers and gravel areas where water is abundant. It is commonly found growing with Liverworts.  Pearlwort is commonly seen growing as a prostrate mat in containers and on gravel around containers. Image by: James Altland, USDA-ARS
Prostrate spurge
Chamaesyce maculata
During Oregon’s typically cooler summers, Prostrate spurge usually becomes problematic only during the hottest part of summer.  Foliage is small, succulent, and often with small red spots. Image by: James Altland, USDA-ARS
Redroot pigweed
Amaranthus retroflexus L.
Redroot pigweed is a summer annual, but commonly germinates throughout the year with adequate moisture. When mature, it usually reaches a he  Redroot pigweed generally grows upright, forming large masses or clumps. Image by: James Altland, USDA-ARS
Scarlet pimpernel
Anagallis arvensis
Although it is not in the same family as the other chickweeds, scarlet pimpernel can also be called red chickweed.  Foliage of scarlet pimpernel is opposite and can reach 1 inch in length. Leaves sometimes may occur in whorls of three. Image by: James Altland, USDA-ARS
Tansy ragwort
Senecio jacobaea
Originally a native of Europe and western Asia, Tansy ragwort is an invasive weed in much of the Pacific Northwest.  Terminal flower clusters contain numerous flower heads consisting of both ray and disc flowers. Image by: James Altland, USDA-ARS
Wild carrot
Daucus carota
Because wild carrot is a biennial, it has a two year life cycle. The first year it forms a rosette of leaves, followed by a second year of f  Flowers stalks emerge from bushy rosette of wild carrot. Image by: James Altland, USDA-ARS
Yellow nutsedge
Cyperus esculentus
Yellow nutsedge is a noxious weed and restrictions on shipping exist for many shipping destinations. It is a serious concern with field grown nursery stock, especially balled in burlap crops.
Yellow woodsorrel
Oxalis stricta
Yellow wood sorrel is a species of Oxalis that is commonly found in nurseries and landscapes throughout Oregon.  Yellow woodsorrel has a rounded mound growing habit and green foliage. Image by: James Altland, USDA-ARS